The present invention relates to bearing means in drill bits for performing crushing type rotary drilling in rock, usually referred to as rotary drill bits. The invention may, however, also be used in other types of rotary drill bits, for instance drill bits for full face drilling of tunnels.
Bearings for roller drill bits are normally built according to either of two basic principles. One of these principles is to provide the bearing construction with seals and to supply the bearings with grease or oil from a small container in each leg of the bit. This bearing construction is usually used in oil drilling where the axial feed forces are moderate. The frictional work and the development of heat in the bearings is small and the temperature in the bearings can be held at a low level. Accordingly, it is not necessary to supply air or any other coolant to the bearing.
The other principle, on which the present invention is based, is that the bearing has no seals and that the drilling takes place with air flushing. This construction is used for blast hole drilling where the load on the bearings is substantial due to the great axial feed force. This necessitates air flushing through the bearings in order to keep the temperature low in the bearings. The air circulation through the drill bit does not permit the use of lubricants as in sealed bearings, because oil and grease in the bearings would not be retained in the bearings under the pressure of the flow of air.
It is known from U.S. Pat. No. 3,151,691 to use a metal harder than steel for axial and radial bearings in sealed drill bits according to the first mentioned basic principle. The drill bit described in the patent is obviously intended to be used for oil drilling. The said harder metal is for both sealed and unsealed bits, usually Stellite, attached by welding.
It is an object of the present invention to provide a plane bearing for unsealed roller drill bits cooled by air flushing, which bearing exhibits both substantially less wear than in the conventional art and a considerable increase in the load carrying capacity of the bearing.